Magnetic tunnel junctions using amorphous materials as reference and free layers

Abstract

Magnetic tunnel junctions are constructed from a MgO or Mg—ZnO tunnel barrier and amorphous magnetic layers in proximity with, and on respective sides of, the tunnel barrier. The amorphous magnetic layer preferably includes Co and at least one additional element selected to make the layer amorphous, such as boron. Magnetic tunnel junctions formed from the amorphous magnetic layers and the tunnel barrier have tunneling magnetoresistance values of up to 200% or more.

1. A method, comprising:
 forming a tunnel barrier selected from the group of tunnel barriers consisting of MgO and Mg—ZnO; 
 forming first and second amorphous ferromagnetic layers in proximity with respective underlayers by depositing Co and at least one other element on each of the underlayers, wherein the amorphous layers and the tunnel barrier are formed in proximity to one another to permit spin-polarized current to pass between the first and second amorphous layers through the tunnel barrier, thereby forming a magnetic tunnel junction, the magnetic tunnel junction having a tunnel magnetoresistance of at least 100% at room temperature; and 
 forming in proximity with the second amorphous layer at least one of the following: i) an antiferromagnetic layer that exchange biases the second amorphous magnetic layer, and ii) an additional magnetic layer and an antiferromagnetic coupling layer in proximity with the second amorphous magnetic layer, so that the additional magnetic layer, the coupling layer, and the second amorphous magnetic layer form a synthetic antiferromagnet reference layer, wherein the coupling layer couples the second amorphous magnetic layer and the additional magnetic layer. 
 
     
     
       2. The method of  claim 1 , wherein said at least one other element includes B. 
     
     
       3. The method of  claim 1 , wherein said at least one other element includes Zr. 
     
     
       4. The method of  claim 1 , wherein said at least one other element includes Hf. 
     
     
       5. The method of  claim 1 , wherein ferromagnetic crystalline layers are in contact with the tunnel barrier, each of the ferromagnetic crystalline layers contacting one of the amorphous layers. 
     
     
       6. The method of  claim 1 , wherein the tunnel barrier is (100) oriented. 
     
     
       7. The method of  claim 1 , comprising annealing the junction to increase its tunneling magnetoresistance. 
     
     
       8. The method of  claim 7 , wherein the junction is sufficiently free of defects and deleterious oxide, that the magnetic tunnel junction has a tunnel magnetoresistance of greater than 120% at room temperature. 
     
     
       9. The method of  claim 7 , wherein the junction is annealed at a temperature selected to yield a tunnel magnetoresistance of greater than 160% at room temperature. 
     
     
       10. The method of  claim 7 , wherein the junction is annealed at a temperature selected to yield a tunnel magnetoresistance of greater than 200% at room temperature. 
     
     
       11. The method of  claim 7 , wherein the junction is annealed at a temperature greater than 260° C. 
     
     
       12. The method of  claim 7 , wherein the junction is annealed at a temperature greater than 300° C. 
     
     
       13. The method of  claim 7 , wherein the junction is annealed at a temperature greater than 340° C. 
     
     
       14. The method of  claim 7 , wherein the junction is annealed at a temperature greater than 380° C. 
     
     
       15. The method of  claim 7 , wherein the junction is annealed at a temperature greater than 400° C. 
     
     
       16. The method of  claim 1 , wherein the tunnel barrier includes a MgO tunnel barrier. 
     
     
       17. The method of  claim 16 , wherein the MgO tunnel barrier is formed by:
 depositing Mg onto a surface of an underlayer to form a Mg layer thereon, wherein the surface is selected to be substantially free of oxide; and 
 directing additional Mg, in the presence of oxygen, towards the Mg layer to form a MgO tunnel barrier in contact with the surface, the oxygen reacting with the additional Mg and the Mg layer. 
 
     
     
       18. The method of  claim 1 , wherein the tunnel barrier includes a Mg—ZnO tunnel barrier. 
     
     
       19. The method of  claim 18 , wherein the Mg—ZnO tunnel barrier is formed by:
 depositing a metal layer onto a surface of an underlayer, wherein the surface is selected to be substantially free of oxide; and 
 directing additional metal towards the metal layer, in the presence of oxygen, to form a magnesium-zinc oxide tunnel barrier in contact with the surface, the oxygen reacting with the additional metal and the metal layer, wherein: 
 
       at least one of the metal layer and the additional metal includes Zn, and 
       at least one of the metal layer and the additional metal includes Mg. 
     
     
       20. The method of  claim 1 , wherein at least one of the amorphous ferromagnetic layers is formed directly on the tunnel barrier. 
     
     
       21. The method of  claim 1 , wherein the tunnel barrier is formed directly on one of the amorphous ferromagnetic layers.